A device of this type is known, for example, from German Published Patent Application No. 101 35 142 and is used, for example, in the intake tract of an internal combustion engine to determine the air-mass flow passed through a conduit to the internal combustion engine. A portion of a sensor device provided with a bypass section is inserted into the conduit member through an insertion opening. The bypass section features a channel structure having an inlet region from which a measuring channel provided with a measuring element branches off. The inlet region further has a separation zone having at least one separation opening which opens into the conduit passage at at least one side wall of the bypass section. The separation zone is used to remove liquid and/or solid particles from the channel structure, thereby preventing them from entering the measuring channel and contaminating the measuring element provided therein.
The bypass section inserted in the conduit has edges which are formed by the front side facing the main flow direction and the side walls and which, in the known devices, form impingement edges where regions of detached flow are formed. These regions of detached flow can cause, on the one hand, high pressures losses and, on the other hand, unintentional flow pulsation, as a result of which pressure fluctuations are transmitted through the separation opening to the measuring channel branching off from the inlet region. The pressure fluctuations in the measuring channel can significantly corrupt the output signal of the measuring element.